Oximeter sensor with digital memory encoding patient data

ABSTRACT

The present invention provides a memory chip for use in an oximeter sensor, or an associated adapter or connector circuit. The memory chip allows the storing of patient related data, such as patient trending data or a patient ID, to provide enhanced capabilities for the oximeter sensor. In addition to providing unique data to store in such a memory, the present invention include unique uses of the data stored in such a memory.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/943,899, filed Aug. 30, 2001 and claims the benefit of U.S.Provisional Patent Application No. 60/229,616, filed Aug. 31, 2000,which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to oximetry sensors and, in particular,pulse oximetry sensors which include coded information relating topatients.

Pulse oximetry is typically used to measure various blood flowcharacteristics including, but not limited to, the blood-oxygensaturation of hemoglobin in arterial blood, the volume of individualblood pulsations supplying the tissue, and the rate of blood pulsationscorresponding to each heartbeat of a patient. Measurement of thesecharacteristics has been accomplished by use of a non-invasive sensorwhich passes light through a portion of the patient's tissue where bloodperfuses the tissue, and photoelectrically senses the absorption oflight in such tissue. The amount of light absorbed is then used tocalculate the amount of blood constituent being measured.

The light passed through the tissue is selected to be of one or morewavelengths that are absorbed by the blood in an amount representativeof the amount of the blood constituent present in the blood. The amountof transmitted light passed through the tissue will vary in accordancewith the changing amount of blood constituent in the tissue and therelated light absorption. For measuring blood oxygen level, such sensorshave been provided with light sources and photodetectors that areadapted to operate at two different wavelengths, in accordance withknown techniques for measuring blood oxygen saturation.

An encoding mechanism is shown in U.S. Pat. No. 4,700,708, thedisclosure of which is incorporated herein by reference. This mechanismrelates to an optical oximeter probe which uses a pair of light emittingdiodes (LEDs) to direct light through blood-perfused tissue, with adetector picking up light which has not been absorbed by the tissue. Theoperation depends upon knowing the wavelength of the LEDs. Since thewavelength of LEDs can vary, a coding resistor is placed in the probewith the value of the resistor corresponding to the actual wavelength ofat least one of the LEDs. When the oximeter instrument is turned on, itfirst applies a current to the coding resistor and measures the voltageto determine the value of the resistor and thus the value of thewavelength of the LED in the probe.

U.S. Pat. No. 5,259,381 recognizes that the coded value of thewavelength of the red LED provided by a coding resistor may beinaccurate, since the actual wavelength can vary with temperature.Accordingly, this patent teaches including a temperature sensor in theoximeter probe to measure the actual temperature. With the actualtemperature, and the coded wavelength value, a look-up table can beconsulted to determine the actual LED wavelength for that temperature.

Another method of storing coded information regarding thecharacteristics of the LEDs is shown in U.S. Pat. No. 4,942,877 assignedto Minolta. This patent discloses using an EPROM memory to store digitalinformation, which can be provided in parallel or serially from thesensor probe to the remote oximeter. The memory is described as storingcoefficients for the saturation equation, wavelength, subwavelength(where 2 peaks for LED), half-width of wavelength spectrum emitted byLED, intensity of LEDS or ratio, and on time of LEDS (written by theprocessor).

Other examples of coding probe characteristics exist in other areas.Multiple calibration values are sometimes required, with this making thecircuitry more complex or requiring many leads. In Patent No. 4,446,715,assigned to Camino Laboratories, Inc., a number of resistors are used toprovide coded information regarding the characteristics of a pressuretransducer. Patent No. 3,790,910 discloses another pressure transducerwith a ROM storing characteristics of the individual transducer. PatentNo. 4,303,984 shows another probe with digital characterizationinformation stored in a PROM, which is read serially using a shiftregister.

Typically, the coding element is mounted in the probe itself. Forinstance, U.S. Pat. No. 4,621,643 shows the coding resistor mounted inthe probe element itself. In addition, U.S. Pat. No. 5,246,003 shows thecoding resistor being formed with a printed conductive material on theprobe itself.

In some devices, an electrical connector coupled by a cable to a deviceattached to a patient may include a coding element. For example, U.S.Pat. No. 3,720,199 shows an intra-aortic balloon catheter with aconnector between the catheter and a console. The connector includes aresistor with a value chosen to reflect the volumetric displacement ofthe particular balloon. U.S. Pat. No. 4,684,245 discloses a fiberopticcatheter with a module between the fiberoptic and electrical wiresconnected to a processor. The module converts the light signals intoelectrical signals, and includes a memory storing calibration signals sothe module and catheter can be disconnected from the processor and usedwith a different processor without requiring a recalibration.

Patent No. 5,645,059 teaches using a modulated signal to provide thecoded data to a remote analyzer. Patent No. 5,429,129 shows using avoltage regulator to produce a specific voltage value in response to anattempt to read by the analyzer.

Hewlett-Packard Company Patent No. 5,058,588 teaches an oximeter sensorwith an encoding element that could be resistor, ROM, or customizedintegrated circuit. The encoding element encodes the type of sensor (inparticular, type indicating area of placement on body—finger, ear, foot,arm; also, the type of sensor can indicate transmission/reflection type,or adult/neonate {indicating correction to be performed on theoreticaloxygen saturation, allow switching between physiological limits such asminimum/maximum pulse rates for adults/neonates}; the maximum drivingcurrent may be adapted according to type of sensor, and contact ofsensor with tissue can be tested by means of an attenuation measurementif sensor type is known).

Nellcor Patent No. 5,645,059, the disclosure of which is herebyincorporated herein by reference, teaches coding information in sensormemory used to provide pulse modulated signal, to indicate the type ofsensor (finger, nose), the wavelength of a second LED, the number ofLEDs, the numerical correction terms to the standard curves, and anidentifier of the manufacturer.

A number of catheter patents also discuss encoding information in thecatheter. Sentron Patent No. 4,858,615 teaches encoding the type ofsensor, type number, serial number, date of production, safe use life ofthe sensor, correction data for non-linearity, pressure sensitivity,offset, and temperature sensitivity.

Interflo Medical Published PCT Application No. PCT/US92/08263,Publication No. WO 93/06776 teaches encoding patient specific data,size, manufacture date, batch number, sterilization date, expirationdate, transducer number and type, manufacturer's name and address,thermistor heating element resistance, filament efficiency, programsegments or patient historical data, format version for the calibrationdata, trademark information, catheter unique serial number, ship date,other date and time information, security code to identify manufacturer,thermal mass, filament composition, coefficient of resistance, layoutbyte, checksum, copyright, number of seconds since a certain date,patient weight, patient height, timestamp of 1st CO data point, and acount of all CO data points in EEPROM.

Dulex-Ohmeda of Boulder, Colo. markets an oximeter sensor product thatencodes data into resistor values representing pointers to a lookuptable containing coefficients (as in U.S. Pat. No. 4,700,708) as well asindicating a range of LED drive current to use with the sensor. The LEDsare driven with a higher or lower drive currents depending upon thevalue of the resistor in a particular sensor.

Honeywell Patent No. 4,303,984 (expires Dec. 14, 1999) describes amemory which stores characterization information, such as linearizationinformation for a pressure sensor. Alnor Instrument Patent No. 5,162,725describes storing both calibration and ID information in a sensormemory. Seimans Patent No. 5,016,198 describes a coding memory in asensor with data for defining sensor's characteristic curve. McBeanPatent No. 5,365,462 describes a date code in a sensor memory. HoneywellPatent No. 4,734,873 describes a pressure sensor with a PROM storingcoefficients for a polynomial. Robert Bosch Patent No. 4,845,649describes a PROM in a sensor storing correcting data.

McBean Patent No. 5,371,128 relates to EEPROM in sensor with sensor typecode and calibration data. McBean Patent No. 5,347,476 describes anaccuracy code. Otax Patent No. 5,528,519 shows a PROM in a connector foroximeter.

Square D Company Patent No. 5,070,732 shows calibration data in a sensormemory. Baxter Patent No. 5,720,293 talks about different calibrationinformation for a catheter, including a security code (encryption isdiscussed), serial number, model number, ID data such as calibration,manufacture, sterilization and ship date or other date and timeinformation, a software program segment, security code for identifyingwhether sensor made by same manufacturer as monitor manufacturer,filament or transducer resistance, heat transfer coefficient, thermalmass, filament composition and coefficient of resistance, layout byte,copyright notice, checksum, random data bytes. Porsche Patent No.5,008,843 describes a sensor with EEPROM ID and characteristics data.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a memory chip for use in an oximetersensor, or an associated adapter or connector circuit. The memory chipallows the storing of patient related data, such as patient trendingdata or a patient ID, to provide enhanced capabilities for the oximetersensor. In addition to providing unique data to store in such a memory,the present invention include unique uses of the data stored in such amemory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a pulse oximeter system in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of a pulse oximeter system incorporating acalibration memory element 56 according to the invention. In oneembodiment, memory element 56 is a two-lead semiconductor digital memorychip. The calibration element is part of the sensor 50 which alsoincludes red and infrared LEDs 52 as in the prior art, along with adetector 54. If desired, LEDs 52 may be replaced with other lightemitting elements such as lasers.

The oximeter includes read circuit 60, drive circuit 66, look-up tables62 and 63, controller 64, amplifier 72, filter 74, and analog-to-digitalconverter 76. Read circuit 60 is provided for reading multiple codedvalues across the two leads 51, 53 connected to calibration element 56.One value is provided to a look-up table 62 to determine appropriatewavelength dependent coefficients for the oxygen saturation calculation,as in the prior art. The other value(s) are then provided to anotherlook up table(s) 63 which provides input (e.g., coefficients) to othercalculations performed by controller 64. These additional calculationsmay enhance the performance and/or safety of the system. Controller 64provides signals to a drive circuit 66, to control the amount of drivecurrent provided to LEDs 52.

As in the prior art, detector 54 is connected through an amplifier 72and a filter 74 to an A/D converter 76. This forms a feedback path usedby controller 64 to adjust the drive current to optimize the intensityrange of the signal received. For proper operation the signal must bewithin the analog range of the circuits employed. The signal should alsobe well within the range of A/D converter 76. For example, one rule thatmay be applied is to adjust LED drives and amplifier gains so that bothred and IR signals fall between 40% and 80% of full scale reading ofconverter 76. This requires correct and independent settings for boththe red and infrared LEDs.

In an embodiment of the present invention, patient-specific data such astrending data or patient monitoring parameters can be actively stored inthe memory of memory chip 56. As the patient and sensor travel fromward-to-ward of the hospital, and consequently plug into differentoximeters, the patient-specific data can be read from memory 56 of thepatient's dedicated sensor and displayed on a display screen for viewingor used by the oximeter monitor for other purposes. Memory 56 may, forexample, be implemented as a random access memory (RAM), a FLASH memory,a programmable read only memory (PROM), an electrically erasable PROM, asimilar programmable and/or erasable memory, any kind of erasablememory, a write once memory, or other memory technologies capable ofwrite operations. Examples of patient specific data that can be storedin memory 56 are now discussed.

Patient trending data regarding the history of a patient's blood oxygensaturation (SpO₂) level, pulse rate, pulse amplitude, perfusion data,and other patient data over a period of time can be recorded in memorychip 56. The oximeter monitor can continuously or periodically store apatient's current trend data into memory 56 to maintain a historicaldata for the patient. The patient trend data can be erased from memory56 each time a sensor is used on a new patient (e.g., each time theoximeter monitor is turned off or when user input to the monitorindicates a new patient). Alternatively, the data encoded into memory 56can be permanent and non-erasable. Further details of a Method andCircuit for Storing and Providing Historical Physiological Data arediscussed in U.S. patent application Ser. No. 09/520,104 to Swedlow etal., filed Mar. 7, 2000, which is incorporated by reference herein inits entirety.

As another example, the lowest and/or highest blood oxygen saturationlevel, pulse rate, pulse amplitude value, temperature data, bloodpressure, perfusion data, or any other patient data during the monitoredtime may be stored in memory 56 by the oximeter monitor. If desired, thelowest/highest values of these patient parameters over a past specifiedmonitoring time (e.g., 2 hours, 1 day, etc.) may be recorded in memory56.

Expected ranges for patient parameters (such as pulse rate, pulseamplitude, and blood oxygen saturation level) that are specific to aparticular patient may also be recorded in memory 56 by a clinician.This can be a desirable feature, because the expected patient trendingdata can vary significantly for each patient. The oximeter monitor cancompare the expected range for the patient stored in memory 56 with themonitored patient trending data to determine if the patient's pulse andblood oxygen levels are within the expected range for that patient. Ifthe monitored patient parameter varies outside the patient-specificrange recorded in memory 56, a warning message may be displayed on theoximeter monitor or alarm signal may be sounded. If desired, anyvariations in the monitored patient parameters from the expected rangesmay be recorded in memory 56 along with a time stamp.

If desired, portions of a patient's medical chart and/or past medicalhistory can be digitally encoded and stored in memory 56 (if sufficientmemory space is available) so that this information is maintained withthe patient as he is moved around and can be easily accessed anddisplayed using an oximeter monitor if the patient transferred to adifferent room or hospital.

The pulse oximeter can keep track of how long a particular patient hasbeen monitored by the pulse oximeter and can periodically store thattime interval in memory 56 by checking the elapsed time on a counter.The counter may be a circuit element in the oximeter monitor that isreset each time the oximeter monitor begins to receive data signals froma sensor or each time that the oximeter monitor is turned off. The timeperiod that a patient has been monitored by the oximeter sensor may bedisplayed on a display screen for viewing.

The pulse oximeter monitor may also include a digital clock that keepstrack of the current date and time. The date and time that the oximetermonitor was turned on and the date and time that the oximeter monitorwas turned off may be encoded into the sensor in memory 56. When theoximeter monitor is turned back on again, the monitor can display thedate and time that it was last turned on and off. It may be desirablefor medical personnel to know the last time that patient's vital signswere monitored by the oximeter.

The oximeter monitor instrument may also write the alarm limits usedwith a particular patient into memory chip 56. Alarm limits are valuesthat represent maximum or minimum values of patient trending datatracked by the oximeter (such as blood oxygen saturation, pulse rate,pulse amplitude, etc.) that will trigger an alarm, because they areconsidered to be dangerous levels. The alarm limit values may be encodedin memory 56 by the manufacturer or by a clinician through the oximetermonitor prior to operation.

The oximeter monitor periodically checks the patient's monitoredtrending data against the alarm limit values. When one of the monitoredpatient parameters reaches the alarm limit value stored in memory 56,the oximeter monitor triggers an alarm which alerts medical personnelthat a problem may exist. The present invention also allowspatient-specific alarm values to be set by medical personnel through theoximeter and stored in memory 56 so that as the patient moves frommonitor-to-monitor (while the sensor stays with the patient), theappropriate alarm limits need not be reset each time on the new monitor.Instead, the alarm limits only need to be programmed once, or at a latertime, whenever the clinician adjusts alarm limits.

One of more of the patient trending data including blood oxygensaturation, pulse rate, and pulse amplitude can be written to memory 56along with a time of occurrence whenever an alarm threshold is crossed.Additional information, such as the readings for a predetermined timeprior to an alarm occurrence can also be stored, and/or periodic valuesduring the alarm breach can also be stored in memory 56.

Currently sensors are placed on patients at one hospital site and staywith the patient from hospital site-to-site. It would therefore bedesirable to have a patient identification code (patient ID) such as aunique number carried along in the sensor so that the record keeping,which occurs at each site, can link the recorded information with thepatient. Without a patient ID stored in the sensor itself, the trackinghas to be done manually. This method is prone to mistakes and increasesthe labor involved in managing the patient.

Thus, in a further embodiment of the present invention the oximetermonitor can store a patient ID in memory 56 of sensor 50. The oximeterhas an input device such as a keyboard, touch screen, or scanner thatallows a patient ID to be entered and reentered into the oximeter sothat it can be stored in sensor memory 56. With patient trendinginformation being stored in memory 56 of the sensor as discussed above,it is also desirable to have the patient ID stored in memory 56 so thatas the patient goes from hospital location to location, the newlocation's staff can verify that old trending information stored inmemory 56 was indeed obtained from that particular patient. Medicalpersonnel can check that the patient ID stored in sensor 50 matches thepatient ID on the patient's chart and other paper documentation toverify that these medical records correspond to the correct patient. Ifdesired, the oximeter sensor can be interfaced with a hospital computernetwork that maintains a database of patient ID numbers to verify theidentify of the patient and to obtain medical records and otherinformation, for the patient stored on hospital databases. The patientID stored in memory 56 provides assurance that any data read from memory56 of the sensor is correlated with the patient they are receiving.

The pulse amplitude of the measured photoplethysmogram is an indirectmeasure of blood perfusion (flow) in the local tissue, changes in bloodpressure, vascular tone, vasoconstriction or dilation, for example, allhave an effect on the pulsatile signal strength observed with a pulseoximeter.

The measured modulation, or other measurement of perfusion, can bestored in memory 56 for patient trending purposes. The oximeter cancompare current modulation and perfusion data with older data frommemory 56 to determine patient trends over time. The patient's pulseamplitude deteriorating over time may reflect a serious condition thatdemands attention. Therefore, it is desirable to store and monitorchanges in a patient's perfusion over time. Also, a maximum or minimumperfusion limit may be stored in memory 56 that represents the maximumor minimum value that the patient's measured perfusion can reach beforethe sensor needs to be moved, repositioned, or adjusted in some otherway. The oximeter can trigger a warning signal or light when a perfusionlimit has been reached or a significant change has occurred.

While the present invention has been described herein with reference toparticular embodiments thereof, a latitude of modification, variouschanges and substitutions are intended in the foregoing disclosure, andit will be appreciated that in some instances some features of theinvention will be employed without a corresponding use of other featureswithout departing from the scope of the invention as set forth.Therefore, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope and spirit of the present invention.It is intended that the invention not be limited to the particularembodiments disclosed, but that the invention will include allembodiments and equivalents falling within the scope of the claims.

1. A sensor comprising: a light emitting element; a light detecting element; and a memory device storing digital data, the digital data comprising a date and time when a monitor coupled to the sensor was turned on or off.
 2. The sensor of claim 1, comprising a connection to a medical facility computer network, the network comprising of at least one oximeter monitor.
 3. The sensor of claim 1, comprising a circuit configured to read data from a device external to the sensor and a circuit configured to write data to the device external to the sensor.
 4. A memory device, comprising: a memory external to an oximeter monitor that exchanges digitally encoded data with the oximeter monitor, the digitally encoded data including a date and time when a monitor coupled to the sensor was turned on or off.
 5. The memory of claim 4, comprising a light emitting element and light detecting element.
 6. A method comprising: transmitting digitally encoded data from a memory of a sensor, the sensor having a light emitting element and a light detecting element, the digitally encoded data comprising a date and time when a monitor coupled to the sensor was turned on or off.
 7. The method of claim 6, comprising reading the date and time when the monitor coupled to the sensor was turned on or off, and storing the date and time in the memory of the sensor.
 8. The method of claim 6, comprising exchanging digitally encoded data with a medical facility computer network, the digitally encoded data including the date and time when the monitor coupled to the sensor was turned on or off.
 9. A monitor comprising: a drive circuit adapted to provide signals to a sensor; a read circuit adapted to read digitally encoded data from a memory of the sensor, the digitally encoded data including a date and time when a monitor coupled to the sensor was turned on and off; and a write circuit adapted to write digitally encoded data to the memory of the sensor, the digitally encoded data including a date and time when a monitor coupled to the sensor was turned on or off.
 10. The monitor of claim 9, comprising a digital clock configured to track current date and time.
 11. The monitor of claim 9, comprising a display screen that displays the time when a monitor coupled to the sensor was turned on and off.
 12. A method of operating a sensor, the method comprising: providing signals to drive circuitry of a sensor; reading digitally encoded data from a memory of the sensor, the digitally encoded data including a time when a monitor coupled to the sensor was turned on or off; and writing digitally encoded data to the memory of the sensor, the digitally encoded data including a time when a monitor coupled to the sensor was turned on or off.
 13. The method of claim 12, comprising displaying the time when a monitor coupled to the sensor was turned on or off.
 14. A system for sensing and monitoring blood oxygen levels, the system comprising: an oximeter sensor comprising a light emitting element, a light detecting element, and a memory device that stores digitally encoded data, the digitally encoded data including a time when a monitor coupled to the sensor was turned on or off; and a monitor configured to read the digitally encoded data from the sensor and to write digitally encoded data to the memory of the sensor, the digitally encoded data including the time when a monitor coupled to the sensor was turned on or off.
 15. The system of claim 14, comprising a display device for displaying data including the time when the monitor coupled to the sensor was turned on or off. 